China Stock Markets Dive in Their Worst Performance in About a Month

Renewed weakness comes ahead of G-20 meeting in Shanghai this week

SHANGHAI—Chinese shares suffered their biggest slump since the carnage at the beginning of this year, in an embarrassing reminder of the country’s challenges just as world leaders gather there for a global meeting.

Shanghai’s benchmark stock index tumbled 6.4% on Thursday, the day before the city hosts a gathering of finance ministers from the Group of 20 industrialized nations. China has been expected to use the G-20 meeting to...